1. Field of Invention
This present invention relates to implements or apparatus for applying pushing or pulling force, specifically to a slidable adjustable screwjack inner member for a lifting jack. Particularly, this present invention relates to a slidable adjustable jacking device mounted on a tongue of a trailer. More particularly, this invention improves the ability to reduce the number of times a hand crank must be rotated to extend a load-carrying member. This device allows a screwjack inner member to be slid inside a tubular outer member and then pinned in a fixed position.
2. Prior Art
There are times when a lifting jack must have a hand crank rotated many times to extend a load-carrying member so that the member or leg makes contact with the ground to transfer weight. Likewise, upon retracting certain lifting jacks, a hand crank of the jackscrew in the lifting jack must be rotated many times. There have been various attempts to extend or retract the load-carrying member of the lifting jack so that the amount of time and the number of times the hand crank has to be rotated is reduced.
In 1910, Erastus Coddington was awarded U.S. Pat. No. 964,394. This historical patent teaches a lifting jack with a slideable sleeve over a stem. A stem is adjustable and supported on a standard. A sleeve rotates in the stem. There are recesses in the sleeve to allow the stem to be adjustable according to vertical slots. The lifting jack height can be adjusted using slots. However, this device is limited to supporting the weight that rests on these small stems.
Israel Gross's U.S. Pat. No. 2,852,229 teaches lifting equipment for jack operations. This invention has a base and a vertically erect post. The post is provided, at spaced intervals, with diametrically extended perforations to permit adjustment of the position of the adjustable header. The adjustable header includes a tubular portion, which surrounds the post and connects with the header. The advantage of this construction is the considerable height obtainable in this assembly and heavy loads can be lifted by the application of a relatively small force at the jack. The disadvantage of this construction is that it is complicated because it uses a regular lifting jack and additional pieces. The pieces are not integral to the lifting jack and the setup is also complicated.
U.S. Pat. No. 3,275,298, Demountable Containers Provided With Jack Legs for Raising or Lowering the Same, was issued to Albert Hand in 1966. Hand relates to heavy-duty devices for raising, supporting and lowering heavy, bulky bodies, which are required to be moved between relatively low and relatively high elevations and to be supported at levels in between. The jack leg includes a reaction base that is vertically adjustable on the standard between a station adjacent to the foot and at least one station spaced above. To permit the adjustment there are holes in the standard. The holes are registerable (able to be aligned) between the standard and the reaction base using a pin. However, this device does not use the jack as the course alignment but rather a standard off to the side. The force must be channeled through a reaction base, creating a weak link in the transfer of the force vector.
In 1969, Burdette Douglass was awarded U.S. Pat. No. 3,595,527, Quickly Retractable and Extensible Jack Construction, which teaches a jack body that adjusts the load-carrying member that is slidable in the jack body. The Douglass patent uses L-shaped slots in the sleeve and radial projections on the jack body to elongate the jack and provide for rough adjustment in the length of the jack. After the rough adjustment is made, a screw arrangement is used to make fine jacking adjustments. But these L-shaped sleeves can only support so much weight. This weakness is similar to Coddington 964,394 because the much force must be transferred to relatively small ‘dog ears’ or stems.
Leroy Scott, in 1978, was granted a patent for “Heavy Duty Lifting Devices” in U.S. Pat. No. 4,068,826. Scott's invention teaches a plurality of engagement positions for the hydraulic piston rod to permit a greater extension of the load-carrying sleeve with respect to the base of the jack. This invention does not, however, uncomplicated the process of raising or lowering items.
In 1979, Francis Linton et al. were issued U.S. Pat. No. 4,176,824, Lifting Apparatus. This invention teaches a fixture made of two side-by-side plates and two bails fastened to a vehicle. The side-by-side plates are provided with two sets of aligned apertures through which pins may be inserted. This device is limited in nature because the bail fasteners are a point of weakness with regard to transferring forces from the thing being lifted to the area where the lifting apparatus transfers its weight.
U.S. Pat. No. 4,238,113, Jacking Device, was issued to Vernon Adams in 1980. Adams teaches a detached slideable column with a plurality of longitudinally spaced holes extending transversely through the column to provide for the rough adjustment of the column. But this device is comprised of an adjustable column that is not integral to the upright vertical housing and places strain on a rough adjusting column.
Dale McMahan's U.S. Pat. No. 4,842,252, Rapidly Extendable Jack, was issued in 1989. This invention teaches a rapidly expandable jack and a course adjustment mechanism using a pin and a hole arrangement with the pin protruding from the outer sleeve through the inner sleeve. But the pin that the invention uses will only support the weight that rest on a small portion of a pin.
Jerry Pittman's U.S. Pat. No. 5,174,550 is a complicated device that teaches a quick release and quick retract jack that features an outer wall of a tubular member that is deformed inwardly forming detents equally spaced along a significant portion of the length of the outer wall. These detents form spaced projections, which extend inwardly from the inner wall into the bore of the tubular member. The detents allow for positioning of the sleeve.
An Internet publication teaches using a “Hi-Lift’ jack that uses pins to adjust the length of travel of a jacking device. But this device does not have a slidable sleeve to reduce the number of rotations.
An Internet publication teaches a square tube jack, but this jack is not slidable out either end of the outer tube. Shelby Industries makes a “8000 # Top Wind Sq Tube Jack, Weld-On, Drop Leg, Black,” but the device, if welded onto a trailer would require an operator to reach below the trailer to remove or insert a pin to fix the leg length.